The nano-sized antimony trioxides(NSb2O3) were modified by in situ polymerization of styrene(St) and in situ copolymerization of vinyl silane(VS) and St,respectively,and then compounded with high impact polystyrene(HIPS) in molten state.The results showed that the surface of NSb2O3 was coated with polystyrene,subsequently the dispersion of NSb2O3 in HIPS matrix is remarkably enhanced.Thereby,the tensile and impact properties of HIPS/Sb2O3 nanocomposites are improved,and there is a critical PS-coating thickness on the surface of NSb2O3.Because the in situ copolymerization of NSb2O3/VS/St is useful for PS to be grafted on the surfaces of NSb2O3,as a result of the enhanced interfacial adhesion between NSb2O3 and HIPS matrix the Young’s modulus,tensile yielding strength and impact strength of HIPS/NSb2O3 nanocomposites are higher than those in HIPS/NSb2O3 nanocomposites modified by the in situ polymerization of NSb2O3/St.